Enter the first day of your last period, the average length of your cycle, and the current date into the calculator to determine your current menstrual cycle phase.

Cycle Phase Calculator

Enter the first day of your last period, your average cycle length, and today’s date.

Cycle Summary
Phase Guidance
Key Cycle Details
Cycle day—
Days since last period—
Days remaining in cycle—
% of cycle complete—
Next period date—
Days until next period—
Estimated ovulation—
Days until ovulation—
Upcoming fertile window—
Luteal phase starts—
Day within current phase—

Related Calculators

Cycle Phase Formula

The menstrual cycle is divided into four phases, and the phase is determined by the current day in the cycle:

  • Menstrual phase: Day 1 (first day of bleeding) through approximately Day 5. Bleeding typically lasts about 5 days.
  • Follicular (proliferative) phase: From Day 1 through ovulation (around Day 14). This phase varies in length (10–16 days), averaging about 14 days.
  • Ovulation: A brief event, typically on a single day (around Day 14) marked by the LH surge and release of the oocyte.
  • Luteal (secretory) phase: Follows ovulation and has a relatively fixed duration of ~14 days (Day 15–28 in a 28-day cycle).

To determine the current cycle phase, calculate the number of days since the first day of the last period and then find the remainder when divided by the cycle length. This will give you the current day in the cycle, which can be used to determine the phase based on the ranges above.

What is a Menstrual Cycle?

The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that make pregnancy possible. The cycle is required for the production of oocytes, and for the preparation of the uterus for pregnancy. The length of a menstrual cycle can vary, but the average is around 28 days.

How to Calculate Your Cycle Phase?

The following steps outline how to calculate your menstrual cycle phase.

  1. First, input the first day of your last period.
  2. Next, input the average length of your menstrual cycle in days.
  3. Then, input the current date.
  4. Click the "Calculate" button to find out the current phase of your menstrual cycle.
  5. The calculator will display the phase: Menstrual, Follicular, Ovulatory, or Luteal.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

First Day of Last Period = 03/01/2023

Average Cycle Length = 28 days

Current Date = 03/15/2023